Ford J1850 PWM

plisskin · 11-30-2006, 04:23 PM

I am trying to build my own OBD-II reader using a PIC. So far I am able to connect to ISO9141-2 and J1850 VPW but am having some trouble with J1850 PWM.

When I send the J1850 PWM message, I cannot get an answer. I have put a scope on Pin 2 and Pin 10 and see the message go out and also a 1 byte IFR being returned from the vehicle approx. 40 us after my message. But no other message is returned from the vehicle.

For example, I transmit 0x61 0x6a 0xf1 0x01 0x00 0x0a which is supposed to read the supported PIDs of the vehicle. All I get back is a 1 byte IFR of 0x1f.

Does anybody know if I am supposed to transmit again after the 1 byte IFR or am I doing something else wrong?

So far, I am using only information that I have found on the internet, such as obddiagnostics.com

Thanks for your help.

plisskin · 12-01-2006, 08:09 AM

Arrgh, it was my own damn fault. Now I am able to read the response...

Trampas · 12-09-2006, 03:37 PM

Check out the code here http://www.sterntech.com/obdii_pic.php it has complete source code and schematics for a PIC based OBDII scanner.

Trampas
www.sterntech.com

JuanaBee · 12-17-2006, 09:05 AM

Can you explain what it was that you did wrong?

obdiiMasterMind · 12-21-2006, 04:51 PM

Quote: Originally Posted by plisskin

I am trying to build my own OBD-II reader using a PIC. So far I am able to connect to ISO9141-2 and J1850 VPW but am having some trouble with J1850 PWM.

When I send the J1850 PWM message, I cannot get an answer. I have put a scope on Pin 2 and Pin 10 and see the message go out and also a 1 byte IFR being returned from the vehicle approx. 40 us after my message. But no other message is returned from the vehicle.

For example, I transmit 0x61 0x6a 0xf1 0x01 0x00 0x0a which is supposed to read the supported PIDs of the vehicle. All I get back is a 1 byte IFR of 0x1f.

Does anybody know if I am supposed to transmit again after the 1 byte IFR or am I doing something else wrong?

So far, I am using only information that I have found on the internet, such as obddiagnostics.com

Thanks for your help.

What "pic" are you referring too? i would like you're knowledge on the j1850 protocol if you have any. are you willing to share you're knowledge? is the pic you're programming something you bought, or something you actually programmed to logg and send data? if you programmed it with assembly etc,, we would defently need to share knowledge.

Trampas · 12-28-2006, 08:09 AM

I have just finished writting up a document about the PWM protocol, send me an email if you want a copy. I will be adding it to my website here soon, www.sterntech.com.

Also on my website you will find firmware for a PIC 18F87xx which implements J1850.

Trampas

manix · 07-11-2007, 06:07 AM

Quote: Originally Posted by plisskin

Arrgh, it was my own damn fault. Now I am able to read the response...

Hi

Could you please explain, how did you fix the problem.
I'm having the same problem with OKI MSM6636. After sending 0x61 0x6A 0xF1 0x01 0x00 the response is only 1 byte long, the value inside received register (at location 0x15) is 0x10.

Any direction will be helpful

manix · 07-13-2007, 04:27 AM

Quote: Originally Posted by manix

Hi

Could you please explain, how did you fix the problem.
I'm having the same problem with OKI MSM6636. After sending 0x61 0x6A 0xF1 0x01 0x00 the response is only 1 byte long, the value inside received register (at location 0x15) is 0x10.

Any direction will be helpful

.. answer to myself

Problem fixed. There was a problem with interrupt handling time-gap. The host CPU periphery was set too slow; so OKI and SPI interaction also. The answer from the ECU was missed and the next IFR was read instead of the previous received answer.